It is desirable in many cases to have accurate estimate of the channel length for the short channel transistors like FinFETs and nano-wires. It is used to compare transistors to each other, to characterize the short channel effects, to characterize the direct source-to-drain tunneling, to model ballistic mobility, which is directly proportional to the channel length, etc. The gate length is easy to measure or extract from a geometry database, as it is defined by the gate patterning mask and subsequent deposition of the gate dielectric and the gate. However, the physical gate length is not a useful value for determining many critical characteristics of a transistor. More important is to know the effective channel length, which is defined as the average distance from source junction to drain junction. The effective channel length can be smaller than the gate length, same, or larger, depending on how transistor is built. Current practice is for engineers to take a close look at the transistor and estimate its effective channel length based on a number of factors. It is desirable to have an algorithm that can reliably determine the effective channel length and exclude human errors and human-to-human variation due to the different “eye-balling” approaches.